1. Field of Invention
The present invention relates to a fin field effect transistors (FinFETs) and a method for manufacturing the FinFETs. More particularly, the present invention relates to a FinFET with a fully silicidated gate electrode and a method for manufacturing thereof.
2. Description of Related Art
FinFETs have been demostrated to have better scalibility than traditional bulk transistors. Generally, the operations of digital circuit depend on the ability to switch MOS devices from an ON state to an OFF state and vice versa. If the threshold voltage for N-type MOS is not much difference from that for P-type MOS even the margin of the ON and OFF state of the N-type MOS seriously overlap with that of the P-type MOS under general operating current, the circuit will be malfunction under specific operating voltage range.
FIG. 1 shows the Id-Vg (drain current versus gate voltage) plots for the conventional FinFETs. It is well known in the art that while a positive voltage, which is higher than the threshold voltage of the N-type MOS, is applied on the gate of the N-type MOS, an N-channel is formed under the gate and between the source and drain, and then the N-type MOS is turned on under a proper bias. Similarly, while a negative voltage, which is lower than the threshold voltage of the P-type MOS, is applied on the gate of the P-type MOS, a P-channel is formed under the gate and between the source and drain, and then the P-type MOS is turned on under a proper bias. However, as shown in FIG. 1, while a positive voltage of about 0.25V is applied on the gate, not only the N-type MOS is turned on, but also there is current of about 10−7 Amp passing through the drain of the P-type MOS. That is, the P-type MOS is also turned on. Similarly, while a negative voltage of about −0.25V is applied on the gate, the P-type MOS is turned on and the N-type MOS is turned on as well. Therefore, it is easily to induce circuit malfunction under this kind of circumstance. Even while the drain current is about of 10−6, which is a general drain current under the normal circuit operation, it is also possible to turn on the P-type MOS and the N-type MOS at the same gate voltage.